William eats at a restaurant and the cost of his meal is $\$21.00$. He would like to leave a $15\%$ tip. What is his total bill including tip?
Solution: The tip amount is equal to $15\% \times \$21.00$ We can find the tip by first calculating a $10\%$ tip and a $5\%$ tip, and then adding those two numbers together. To calculate a $10\%$ tip, move the decimal point in $\$21.00$ one place to the left. $10\%$ $\times \$21.00$ $\$2.10$ To calculate a $5\%$ tip, divide the $10\%$ tip amount in half. $5\%$ $\times \$21.00 = $ $\$2.10$ $ \div 2 = $ $\$1.05$ Adding the two amounts together gives us $\$2.10$ $\$1.05 =$ $ \$3.15$ The cost of the meal plus the amount of the tip will equal the total bill amount. $\$21.00 + \$3.15 = $ $\$24.15$ The total cost of the bill is $\$24.15$.